I think I'm beaten now
I located the other two screws, once I knew where to look. I cannot achieve simultaneous vertical and horizontal collimation. The best I can do when I centre a distant object in the middle of the left hand view is to have it half way between the centre and the left edge in the right hand view. Each screw does to that side's image what it is supposed to do. I think something else is wrong - a mis-aligned objective lens, perhaps - a prism not seated properly. The exit pupil for the left barrel never becomes a clean round circle - it stays a "cat's eye" through all adjustments of that side - that is suspicious. But nothing rattles and no problem is obvious to my eyes.
My twisted brain can snap the two images into one (in the centre) but the owner's ordered brain cannot.
I still have some poorly focused edges in both views. The centre focus drive is also showing a bad spot.
I think it's off to the Binocular Repair Shop for a good checkup.
Can anyone give a recommendation for a Melbourne repairer? Please?